1. Field of the Invention
The invention relates in general to a stopper assembly for use with a syringe and, more particularly, to a stopper assembly having a positive displacement feature for use with a pre-filled syringe such as those used in flush applications. The invention also relates to a plunger rod and an attachment member adapted for attachment with a stopper assembly.
2. Description of Related Art
Pre-filled syringes, such as those used in flush applications, are typically filled with a saline solution and are used to flush catheters. Example pre-filled syringes are shown in U.S. Pat. Nos. 6,361,524 and 6,743,216, which are incorporated herein by reference and which are directed to syringe assemblies for flush applications. At the end of the flushing procedure, the nurse or technician bottoms out the stopper in the syringe barrel. The process of bottoming the stopper in the barrel can cause a phenomenon known as reflux. Reflux is the reversal of fluid flow up through the catheter, usually due to the spring back of the stopper at the end of a flush injection. This occurs because the stopper compresses to force out additional saline, and subsequently springs back to shape. This causes the syringe to pull saline back into the syringe. This reflux can also pull blood back into the catheter, clogging it. This phenomenon of reflux is detrimental to the maintenance of the catheter line. Accordingly, it is desirable to reduce or eliminate reflux within the syringe.
Existing stopper designs typically include a constant diameter seal and a constant stopper-to-barrel interference to create a seal that will prevent fluid housed inside the barrel from leaking past the front seal of the stopper. The contact pressure of the seal is determined by the interference in these designs, and has to be sufficiently high enough such that they will not leak under the highest possible fluid pressure inside the barrel. The disadvantage of this traditional design is that the higher contact pressures lead to higher static and dynamic frictional forces. Static friction is commonly referred to as break loose force. Additionally, these existing stoppers typically include tip designs that are not self-centering. Because the tips are not self-centering, they do not form a positive seal with the inside back of the luer taper when subjected to axial forces.
Existing stopper designs have attempted to prevent the flow of fluid from the catheter back into the syringe when the clinician does not use a recommended positive pressure flushing technique, and release the force from the plunger rod prior to clamping the catheter. As discussed above, blood entering back into the distal catheter lumen is known as reflux and this reflux can lead to clogged catheters. These previous designs focused on preventing spring-back of the stopper that would create a vacuum to draw fluid back into the syringe. These designs, while effective in reducing reflux, do not consistently prevent all reflux from occurring.
Pre-filled syringes are typically manufactured in an automated process. The process of manufacturing these pre-filled syringes includes the steps of molding the syringe barrel, attaching the cap, filling the barrel, inserting the stopper, sterilizing the filled syringe, then inserting the plunger rod. Because the filled syringes are typically sterilized in an autoclave, size of the syringe is an issue. For this reason, the syringe is typically sterilized prior to the insertion of the plunger rod. Commonly used plunger rods are those of a snap-fit design, attached to the stopper prior to inserting the stopper into the barrel, or a threaded design, attached to the stopper after the stopper has been inserted into the barrel. Plunger rods assembled into the stopper after the stopper has been inserted into the barrel require a significant amount of force to be applied thereto during insertion. Axial forces applied to the plunger rod can cause the rod to become dislodged from the stopper, be misaligned, and/or break. Additionally, currently used snap-fit and/or threaded plunger rods occasionally become dislodged from the stopper during use.
Traditional plunger rods are typically cylindrical members, which are formed from a molded material. These known rods may have a ridged surface wherein four ribs, positioned 90° degrees with respect to one another, form the ridged surface. In this current four ribbed design, a user may apply a side load during flushing or aspiration that may be normal to the edge of the rib, causing minimal side loading deflection, or normal to the region between the ribs (45° from a rib), causing maximum side loading deflection. Additionally, the solid design of the stopper rod adds unnecessary material costs to the rod and may undesirably flex in an axial direction during use.